The present invention relates to a magnetohydrodynamic device (MHD) which can be used as an actuator to enter a torque, or to sense relative rotational motion.
MHD devices have been developed and used to sense relative rotational motion of an inertial mass with respect to a case. According to prior U.S. patents by the inventor, including U.S. Pat. Nos. 4,718,276, 5,067,351 and 6,173,611, the motion of a sensor about a rotational axis may be detected as a voltage potential representing displacement, velocity, or acceleration about the axis. As set forth in these prior patents, a static magnetic field is arranged perpendicular to a liquid proof mass such as mercury, enclosed within a cylindrical channel. The cylindrical channel has an inside circumference, bearing one electrode, and an outside circumference bearing a second electrode. Due to rotation of the case about the axis of the liquid mass, a voltage is created across the electrodes which represents the displacement in radians of the mass in response to rotational movement of the cylindrical channel with respect to the liquid mass. By detecting the first differential of the voltage, and the second differential voltage, it is possible to obtain velocity and acceleration values of the imparted rotation.
MHD devices can also be operated as a torque producer. By applying a voltage across the channel, a force can be induced between the liquid mass and the channel which provides a torque to the channel vis-à-vis the liquid.
The present invention seeks to provide an MHD device which can both sense relative displacements between an internal liquid proof mass, and a channel containing the device, as well as impart a rotational torque between the liquid mass and dowel containing the liquid mass for applications requiring stabilization. This includes an application for providing active torque to cancel disturbances which are incident to a platform which is subject to vibrational forces or jitter. The MHD actuator has the capability of generating a reaction torque due to the heavy inertial fluid within the channel, and can transfer for angular momentum of the channel to a supporting surface to effectively cancel any disturbances to the platform. Applications in which the torque generation may be used for stabilization include inertial reference unit platforms, fast-steering mirrors line of sight controls, beam steering, scanning control, small satellite attitude control and active structural damping.
In the application of providing for stabilization, it is not only necessary to generate the required disturbance producing counter torque, but it is also required to sense the disturbances themselves, so that the torque of the appropriate magnitude can be applied to the platform to effectively cancel the sensed disturbances.